As an infrared detection device that is formed with a semiconductor material and detects infrared rays, for example, there has been an infrared detection device in which infrared absorption layers are formed with an InAs/GaSb superlattice (T2SL) structure on a GaSb substrate. The InAs/GaSb superlattice structure has a type-II band lineup. Thus, adjustment of the film thickness and period of the superlattice enables detection of infrared rays from middle infrared (middle wave (MW)) with wavelengths of 3 to 5 μm to far infrared (long wave (LW)) with wavelengths of 8 to 10 μm.
As an infrared detection device that is capable of detecting two different wavelength bands (for example, middle infrared and far infrared), a two-wavelength type infrared detection device has been disclosed in which infrared absorption layers are formed with a T2SL structure on a GaSb substrate (for example, T. Stadelmann et al., “Development of Bi-Spectral InAs/GaSb Type II Superlattice Image Detectors”, Proc. of SPIE, Vol. 9070, 9070V-1, 2014). However, because the minority carrier lifetime in the T2SL structure is shorter than the value that is originally estimated from the materials, the sensitivity of the two-wavelength type infrared detection device with the T2SL structure is lower than the value that is usually estimated.
On the other hand, an infrared detection device in which the infrared absorption layers are formed with InAsSb bulk mixed crystals has been expected for a longer minority carrier lifetime and higher sensitivity at the same film thickness than the infrared detection device with the T2SL structure. Because InAsSb has large band gap bowing, it is possible to detect infrared rays from middle infrared to far infrared by changing Sb composition. A two-wavelength type infrared detection device has been disclosed which uses such an InAsSb bulk mixed crystal for the infrared absorption layer (For example, N. Baril et al., “Bulk InAsxSb1-x nBn photodetectors with greater than 5 μm cutoff on GaSb”, APL, 109, 122104, 2016 and D. Wang et al., “Infrared emitters and photodetectors with InAsSb bulk active regions”, Proceedings of SPIE, 8704, 870410-1, 2013). InAsSb does not have a crystal substrate that provides lattice match. Thus, when this two-wavelength type infrared detection device is fabricated, a metamorphic buffer (MB) layer is formed with InAlSb or the like on the GaSb substrate or the like, and crystal growth of InAsSb is thereafter caused.
Japanese Laid-open Patent Publication No. 2008-85265 is an example of related art.
W. L. Sarney et al., “Structural and luminescent properties of bulk InAsSb”, JVSTB, 30, 02B105-2, 2012 is also an example of related art.
Incidentally, in the two-wavelength type infrared detection device in which the infrared absorption layers are formed with the bulk mixed crystals, the metamorphic buffer layer is also formed between an infrared absorption layer that detects middle infrared and an infrared absorption layer that detects far infrared. However, the metamorphic buffer layer has many crystal defects. Carriers produced in either one of the infrared absorption layers for middle infrared and far infrared pass through the metamorphic buffer layer formed between those infrared absorption layers, and the detection sensitivity to infrared rays are thus lowered.
Accordingly, as the two-wavelength type infrared detection device in which the infrared absorption layers are formed with the bulk mixed crystals, an infrared detection device is requested which may detect infrared rays in both wavelength bands with proper sensitivity.
An infrared detection device of the present disclosure may obtain proper detection sensitivity to each wavelength band in an infrared detection device in which infrared absorption layers are formed with bulk mixed crystals and which is capable of detecting two or more wavelength bands.